debug(action_cable): add server-side broadcast logging

- Log channel remapping and data on every broadcast
- Log warnings when channel format is unknown
- Helps trace whether broadcasts reach ActionCable.server

lib/mozo/broadcaster/action_cable.rb

@@ -30,8 +30,12 @@ module Mozo
         data    = message[:data]    || message['data']
 
         remapped = remap_channel(channel)
-        return unless remapped
+        unless remapped
+          Rails.logger.warn("[ACTION_CABLE] broadcast skipped: unknown channel #{channel}")
+          return
+        end
 
+        Rails.logger.debug("[ACTION_CABLE] broadcasting to #{remapped}: #{data.inspect}")
         ::ActionCable.server.broadcast(remapped, data)
       rescue => e
         Rails.logger.error("[ACTION_CABLE][ERROR] #{e.message}")